Polyhydroxyalkanoates (PHAs) are biosynthetic plastic materials, and PHAs are capable of being synthesized through ingesting matrix by microbial species present in an environment containing a carbon source and limited nutrients, such as nitrogen, phosphorous, sulfur, oxygen, magnesium, etc. Its excellent thermoplasticity and biodegradability make it possible for the idea which replaces the petroleum-derived plastic with this biosynthetic plastic.
As a result, many research groups have devoted their research to this and have proposed various methods for extracting PHAs. For example, U.S. Pat. No. 7,378,266 provides an improved Process for the solvent-based extraction of PHAs from biomass, comprising the steps of: a) combining the biomass containing the PHAs with a solvent selected from lower chain ketones, and mixtures thereof to form a biomass liquor wherein the biomass liquor comprises less than about 25% water; b) mixing the biomass liquor at a temperature in the range of from about 70° C. to about 120° C.; c) separating the PHAs from the biomass liquor to form a PHA-enriched liquor, wherein the separating occurs at a temperature of at least about 40° C.; d) mixing the PHA-enriched liquor with water to form precipitated PHAs and an impure solvent liquor, wherein the water is mixed with the PHA-enriched liquor in the ratio of from at least about 3 parts water to one part PHAs; and e) recovering the precipitated PHAs from the impure solvent liquor.
In addition, the Taiwan patent No. 1399345 provides a method for extracting polyhydroxyalkanoates from waste sludge, which is to measure the weight of the solid part in the sludge after removing of the sand grain from the collected waste sludge containing microbial cells, and carry out the steps of washing, water removal and freezing so as to stop the microbial cells activity; Subsequently, the sludge is made to carry out a pre-process step to destroy the cell bodies of the microbial cells in the waste sludge performed by freezing; and then the sodium hypochlorite aqueous solution is added into the sludge to prepare a sludge mixture with solid/liquid ratio at 0.67 to 4 mg/ml, so that the cell walls of the microbial cells are destroyed to release the polyhydroxyalkanoates. Finally, the sludge mixture is made to carry out a purification step to remove the non-polyhydroxyalkanoate substance and obtain a purified polyhydroxyalkanoates precipitate.
U.S. Pat. No. 7,378,266 discloses that extracts PHAs by solvent extraction from biological systems such as plants or bacteria. While the Taiwan Patent No. 1399345 can extract polyhydroxyalkanoate with high purity directly from the waste sludge without the condition of carrying out the pure culture. However, both the above two cases require the use of considerable amounts of chemicals to destroy microbial cells to achieve the purpose for extracting PHAs. Next, the current production costs of PHAs are very high, which limits the possibility of industrial production of PHAs and cannot be widely used. In addition, general chemical extraction process need more time, and are not advantageous to commercialization. As a result, there is an urgent need to develop a more economical method of producing PHAs, both the steps and costs thereof meet the requirements of the acceptable range of industrial production.